TWI784761B - Lead-free and antimony-free solder alloys, solder balls, and solder joints - Google Patents

Abstract

The present invention provides lead-free and antimony-free solder alloys, solder balls, and solder joints that increase the shear strength by making the crystal grains at the bonding interface finer and can suppress unfused. The lead-free and antimony-free solder alloy has 0.1~4.5% Ag, 0.20~0.85% Cu, 0.2~5.00% Bi, 0.005~0.09% Ni, 0.0005~0.0090% Ge, and the rest It is an alloy composition composed of Sn, and the alloy composition satisfies the following formula (1) and the following formula (2). 0.013≦(Ag+Cu+Ni+Bi)×Ge≦0.027 (1) Formula Sn×Cu×Ni≦5.0 (2) formula In the above-mentioned formula (1) and the above-mentioned formula (2), Ag, Cu, Ni, Bi, Ge and Sn are the content (mass %) of each alloy composition.

Description

Lead-free and antimony-free solder alloys, solder balls, and solder joints

The present invention relates to lead-free and antimony-free solder alloys, solder balls, and solder joints.

In recent years, electronic devices have been required to be highly integrated, large-capacity, and high-speed. For example, semiconductor packages such as QFP (Quad Flat Package) are used to achieve high integration and high functionality at the semiconductor chip level. The manufacture of QFP adopts the packaging process of bonding the silicon chip cut out from the silicon wafer to the lead frame.

The QFP obtained by bonding tiny electrodes such as BGA (Ball Grid Array) forms solder joints by bonding the silicon chip and the lead frame with a solder alloy. In order to improve the wettability of the solder to the silicon wafer and increase the adhesion strength, it is formed, for example, on a backing metal with a Ni layer on the outermost layer. However, when the Ni layer of the outermost layer comes into contact with molten solder, the Ni layer is melted in the molten solder and Ni corrosion occurs. Here, in order to suppress the diffusion of Ni to the silicon wafer, a barrier layer such as Ti is usually formed on the back metal. If the Ni corrosion proceeds to expose the Ti layer, the wettability of the solder alloy to Ti is very poor, so the backing metal will bounce off the wetness of the molten solder. And even if the Ni layer remains slightly, Ni atoms diffuse into the molten solder while Ti hardly diffuses into Ni. Therefore, at the interface between the Ti layer and the Ni layer in the barrier layer, pores are increased at the atomic level, and the adhesion strength at the interface between the slightly remaining Ni layer and the Ti layer is extremely reduced. As a result, the impact resistance and heat cycle resistance of the junction after die bonding may be poor. In this way, it is extremely important for die bonding to leave the Ni layer of the backing metal.

Also, the tiny electrodes such as BGA use solder balls to form solder bumps. In the case of using solder balls, adhesive flux is applied to tiny electrodes, and solder balls are placed on the flux-coated electrodes. Subsequently, the solder balls are melted by heating in a reflow furnace, and the tiny electrodes are wetted by molten solder to form soldering bumps on the tiny electrodes. So in the case of using solder balls, wettability with electrodes is required.

However, in the past, in addition to the widely used Sn-Ag-Cu solder alloy in the form of solder balls, it is also used for die bonding. However, in the case of using these solder alloys, it is necessary to improve heat cycle resistance, impact resistance, and discoloration resistance due to various demands in recent years. Therefore, regarding the Sn—Ag—Cu solder alloy widely used in the past, various examinations have been conducted in order to improve these characteristics.

For example, Patent Document 1 discloses a Sn-Ag-Cu solder alloy containing Ni as an optional element and Ge as an optional essential element. It is also revealed that when the solder alloy contains Ni, it exhibits heat cycle resistance, and when it contains Ge, it exhibits impact resistance or discoloration resistance. [Prior Art Literature] [Patent Document]

Patent Document 1: Japanese Patent No. 4144415

[Problem to be solved by the invention]

As described above, the solder alloy disclosed in Patent Document 1 is an excellent alloy capable of exhibiting three effects of impact resistance, discoloration resistance, and heat cycle resistance at the same time. However, there is still room for further improvement in alloy design.

Although each element of the solder alloy has an inherent meaning of addition, it is a combination of all constituent elements. Since each constituent element affects each other, the constituent elements must be contained in a well-balanced manner as a whole. The content of each constituent element of the solder alloy system described in Patent Document 1 was individually optimized, and it was considered sufficient to obtain the effects described in Patent Document 1 at the time of filing of Patent Document 1. However, solder alloys having the same constituent elements must contain the constituent elements in a well-balanced manner in addition to individually optimizing the content of each constituent element in order to simultaneously improve each characteristic in response to demands in recent years.

The invention described in Patent Document 1 is an alloy design that assumes the case where solder balls are mounted on microscopic electrodes such as BGA. In addition, even when the solder alloy disclosed in Patent Document 1 is used for die-bonding with a wide bonding area, fracture due to external stress cannot be ignored. Therefore, in the case of soldering using a Sn-Ag-Cu-Ni-Ge solder alloy, it is required to increase the shear strength. Furthermore, the paste applied to the substrate electrode and the solder balls of the BGA are not mixed when they are melted, and the boundary between the paste and the solder balls remains and unfused occurs. Since this is a serious joint failure, it must be suppressed.

In this way, due to the high integration, large capacity, and high speed of electronic equipment in recent years, it is required not only to be suitable for BGA soldering, but also to be suitable for solder alloys for die-bonding used in QFP.

The object of the present invention is to provide lead-free and antimony-free solder alloys, solder balls, and solder joints that increase shear strength and suppress non-fusion by making crystal grains at the bonding interface finer. [Means to solve the problem]

The solder alloy system is composed of two or more elements, and individual individual effects may affect the overall properties of the solder alloy. As mentioned above, since all the constituent elements are integrated, each constituent element is related to each other. The inventors of the present invention focused on alloy design so as to improve shear strength and suppress non-fusion even if the same constituent elements as the solder alloy described in Patent Document 1 can be used not only for BGA but also for QFP. Specifically, the inventors of the present invention conducted a detailed composition study in consideration of the balance of each constituent element in addition to re-examining the meaning of addition of each constituent element.

In addition, when Pb is buried after being used in a substrate in the past, Pb may be eluted by acid rain and may flow into groundwater. In addition, groundwater accumulates in domestic animals or humans to affect the human body. Therefore, Pb is designated as a restricted substance in accordance with the RoHS Act. Furthermore, in recent years, not only Pb, but also Sb, which improves the thermal cycle performance of Sn-based solder alloys, has been increasingly requested to avoid the use of Sb based on environmental and health reasons. A review of alloy compositions to achieve desired properties.

First, the inventors of the present invention examined the lack of fusion in which welding does not occur. The occurrence of non-fusion is caused by the state of the solder ball on the BGA side and the paste on the substrate side. If a thick Sn oxide film is formed on at least one of the solder ball and the paste, it is difficult for the solder alloys to mix with each other during melting, and it may become a boundary between the solder ball and the paste after cooling. As a method of removing the oxide film on each surface, flux is used. However, it is difficult to completely remove the oxide film using flux, and the wettability is deteriorated due to the remaining oxide film.

However, although flux is contained in the paste, it is difficult to remove the oxide film and improve the wettability at the same time. And since the solder ball volume is several times larger than the solder powder volume used in the paste, it is appropriate to solve the non-fusion on the solder ball side rather than on the paste side.

Therefore, it is examined to suppress the occurrence of non-fusion by the alloy composition of the solder ball side. It is known that in Sn-Ag-Cu-Bi-Ni-Ge solder alloy, in order to suppress the formation of Sn oxide film on the surface, the Ge content must be adjusted to an optimum range. Ge is known to absorb oxygen in the atmosphere to form germanium oxide. Germanium oxide forms a hard and brittle oxide film on the surface of the molten solder, but the oxide film is also easily destroyed by the convection of the molten solder itself or the external pressure applied to the molten solder when the chip is placed on the molten solder. Therefore, the fusion of the solder balls and the solder powder in the paste is not hindered. And if the total amount of Ag, Cu, Bi, and Ni content is appropriate, ΔT will be in an appropriate range. Furthermore, the solder powder of the paste and the BGA solder balls are fused by adjusting the viscosity of the molten solder.

In view of these, in the Sn-Ag-Cu-Bi-Ni-Ge solder alloy, the balance of the total amount of Ag, Cu, Bi, and Ni content and the Ge content was investigated in detail to cause fusion. As a result, the insight was gained that non-fusion does not occur when the equilibria are within specific ranges.

The inventors of the present invention examined miniaturization of the intermetallic compound formed at the joint interface in order to improve the joint strength of the solder joint in addition to preventing non-fusion. In order to form a compound of Cu and Sn at the joint interface, the content ratio of Cu and Sn must be in a specific range. In addition, in the compound of Cu and Sn, the miniaturization of the compound is achieved by substituting a part of Cu with Ni. Furthermore, since the liquidus temperature of the solder alloy varies greatly depending on the Cu and Ni contents, it is examined to control the viscosity during melting and suppress the growth of the Sn compound so that ΔT does not become too large. As a result, it was also discovered that in the Sn-Ag-Cu-Bi-Ni-Ge solder alloy, by containing Sn, Cu, and Ni in a well-balanced content, the ΔT is controlled and the metal formed at the joint interface The inter-compound becomes finer, which increases the shear strength.

As a result of active examination focusing on these, it was found that the addition of Bi to the Sn-Ag-Cu-Ni-Ge solder alloy suppresses Ni corrosion. Therefore, as mentioned above, by satisfying the specific relationship between the total amount of Ag, Cu, Bi, and Ni content and the Ge content, the suppression of non-fusion can also be satisfied at the same time. Furthermore, it was also found that when Sn, Cu, and Ni are well-balanced, the shear strength is improved. The present invention obtained from these findings is as follows.

(1) A lead-free and antimony-free solder alloy, characterized in terms of mass%, with 0.1-4.5% Ag, 0.20-0.85% Cu, 0.2-5.00% Bi, 0.005-0.09% Ni, 0.0005% ~0.0090% Ge, the rest is an alloy composition of Sn, the alloy composition satisfies the following formula (1) and the following formula (2), 0.013≦(Ag+Cu+Ni+Bi)×Ge≦0.027 (1) Formula Sn×Cu×Ni≦5.0 (2) formula In the above-mentioned formula (1) and the above-mentioned formula (2), Ag, Cu, Ni, Bi, Ge and Sn are the content (mass %) of each alloy composition.

(2) Lead-free and antimony-free solder alloys as in (1) above, wherein the alloy composition contains 0.0005~0.0045% Ge by mass %. (3) Lead-free and antimony-free solder alloys as described in (1) above or (2) above, wherein the alloy composition, in mass %, each contains 0.01% as the upper limit and is selected from the group consisting of Mn, Pd, P, Au, Pt, One or more species from the group consisting of Cr, Fe, Co, V, Mo, and Nb.

(4) A solder ball made of the lead-free and antimony-free solder alloy according to any one of the above (1) to the above (3). (5) Solder balls as in (4) above, wherein the average particle size is 1 to 1000 μm. (6) The solder ball as in (4) or (5) above, wherein the true sphericity is 0.95 or more. (7) The solder ball as described in (4) above or (5) above, wherein the true sphericity is 0.99 or more.

(8) A ball grid array formed using the solder balls described in any one of (4) to (7) above. (9) A solder joint made of the lead-free and antimony-free solder alloy according to any one of the above (1) to (3).

The present invention is described in detail below. In this specification, "%" related to the solder alloy composition is "mass%" unless otherwise specified. 1. Alloy composition (1) 0.1~4.5% Ag Ag is an element that increases the strength of the solder alloy by precipitating fine Ag ₃ Sn at the grain boundaries. When the Ag content is less than 0.1%, the effect of adding Ag cannot be fully exerted. The lower limit of the Ag content is at least 0.1%, preferably at least 0.5%, more preferably at least 1.0%, even more preferably at least 2.0%, particularly preferably at least 2.8%, most preferably at least 3.0%. On the other hand, if the Ag content is too high, coarse Ag ₃ Sn will be precipitated, deteriorating the strength. The upper limit of the Ag content is 4.5% or less, preferably 4.0% or less, more preferably 3.8% or less, still more preferably 3.5% or less, most preferably 3.2% or less.

(2) 0.20~0.85% Cu Cu is an element that can inhibit Cu corrosion and achieve precipitation strengthening through Cu ₆ Sn ₅ . If the Cu content is less than 0.20%, the amount of Cu ₆ Sn ₅ precipitated is small, and a brittle SnNi compound is precipitated, so the solder alloy itself becomes brittle. The lower limit of the Cu content is more than 0.20%, preferably more than 0.3%, more preferably more than 0.4%, more preferably more than 0.5%, more preferably more than 0.6%, particularly preferably more than 0.7%, and most preferably more than 0.75% above. On the other hand, when the Cu content exceeds 0.85%, the liquidus temperature of the solder alloy becomes high, making it difficult to melt. The upper limit of the Cu content is 0.85% or less, preferably 0.80% or less.

(3) 0.2~5.00% Bi Bi is an essential element in the solder alloy of the present invention because by adding a certain amount, the mechanical properties of the shape of the solder balls most suitable for BGA can be obtained. Bi improves mechanical properties through solid solution strengthening, and can also improve creep resistance or wettability. Furthermore, the crystal structure of (Cu,Ni) ₆ Sn ₅ is deformed by the solid solution of Bi in Sn, and the corrosion of Ni can be suppressed by coexistence with Ge. Bi must be contained at least 0.2%, preferably at least 0.3%, more preferably at least 0.5%, more preferably at least 1.0%, particularly preferably at least 1.4%, most preferably at least 1.5%.

On the other hand, when Bi is added in excess, the drop resistance may deteriorate. Furthermore, since the solidus temperature decreases while the liquidus temperature hardly changes, ΔT of the difference between the liquidus temperature and the solidus temperature increases. If ΔT is too large, segregation will occur during solidification, resulting in a decrease in mechanical properties such as mechanical strength. Therefore, the upper limit of the Bi content must be 5.00% or less, preferably 4.0% or less, more preferably 3.5% or less, more preferably 3.0% or less, particularly preferably 2.5% or less, most preferably 2.0% or less.

(4) 0.005~0.090% Ni Ni is an element that can control the liquidus temperature of the solder alloy and inhibit Ni corrosion similarly to Cu. When the Ni content is less than 0.005%, it is difficult to exhibit the effect of Ni addition. The lower limit of the Ni content is at least 0.005%, preferably at least 0.01%, more preferably at least 0.02%, even more preferably at least 0.03%, and most preferably at least 0.04%. On the other hand, when the Ni content exceeds 0.090%, the liquidus temperature of the solder alloy becomes high, making it difficult to melt. The upper limit of the Ni content is 0.090% or less, preferably 0.080% or less, more preferably 0.070% or less, still more preferably 0.068% or less, particularly preferably 0.060% or less, most preferably 0.050% or less.

(5) Ge of 0.0005~0.0090% Ge is an element that can suppress unfused and Ni corrosion. When Ge is not contained, tin oxide is formed on the surface of molten solder. Tin oxide is strong and difficult to break. On the other hand, Ge added to the solder alloy reacts with O in the environment to form a hard and brittle oxide film on the surface of the molten solder. Since this oxide film is brittle, it is easily broken by convection of the molten solder itself or by external force applied from the chip when the chip is mounted. Therefore, it can hinder the formation of the oxide film of Sn and not maintain the oxide film on the surface of the molten solder. Contrary to the oxide film of Sn, it can promote the fusion of the solder ball and the solder powder in the paste.

In addition, Ge is an element capable of solid-solving Ni in (Cu,Ni) ₆ Sn ₅ formed at the bonding interface and suppressing Ni corrosion. Since (Cu,Ni) ₆ Sn ₅ is formed at the joint interface, the crystal structure of the compound is deformed by Ge, and the movement of Ni in the compound is suppressed, thereby inhibiting the movement of Ni to the solder alloy. When Ge is not included, since the crystal structure of (Cu,Ni) ₆ Sn ₅ is maintained in an aligned state, Ni at the joint interface diffuses in the solder alloy, and Ni corrosion occurs.

If the Ge content is less than 0.0005%, tin oxide will be formed, and the crystal structure of (Cu,Ni) ₆ Sn ₅ is not deformed, so it is difficult to exert the above-mentioned effects. The lower limit of the Ge content is at least 0.0005%, preferably at least 0.0020%, more preferably at least 0.0030%, and more preferably at least 0.0035%. On the other hand, when the Ge content is too large, the liquidus temperature becomes high and melting becomes difficult. The upper limit of the Ge content is 0.0090% or less, preferably 0.0080% or less, more preferably 0.0060% or less, still more preferably 0.0050% or less, particularly preferably 0.0045% or less, most preferably 0.0040% or less.

(6) Containing one or more selected from the group consisting of Mn, Pd, P, Au, Pt, Cr, Fe, Co, V, Mo, and Nb with an upper limit of 0.01% each The solder alloy of the present invention may contain at least one selected from Mn, Pd, P, Au, Pt, Cr, Fe, Co, V, Mo, and Nb as optional elements with an upper limit of 0.01%. These elements improve mechanical properties.

(7) Rest: Sn The remainder of the solder alloy of the present invention is Sn. Inevitable impurities may also be contained in addition to the aforementioned elements. When unavoidable impurities are contained, the aforementioned effects are not affected. Specific examples of unavoidable impurities include As and Cd. Also, although the present invention is lead-free and antimony-free, it does not exclude the inclusion of Pb or Sb as unavoidable impurities. If In is contained, the wettability deteriorates, so it is preferable not to contain it. In addition, since Mn is oxidized at the time of solder alloy production and it is difficult to produce a solder alloy, it may not be contained.

(8) (1) formula The present invention satisfies the following formula (1). 0.004＜(Ag+Cu+Ni+Bi)×Ge＜0.032 (1) formula In the above formula (1), Ag, Cu, Ni, Bi, and Ge are the contents (% by mass) of the respective alloy compositions.

If formula (1) is satisfied, non-fusion is suppressed. In the Sn-Ag-Cu-Bi-Ni-Ge solder alloy, as mentioned above, Ge absorbs oxygen in the atmosphere to form hard and brittle germanium oxide. The oxide film is also easily destroyed by convection of the molten solder itself or external pressure applied to the molten solder when the chip is placed on the molten solder. Therefore, it can hinder the formation of the oxide film of Sn and not maintain the oxide film on the surface of the molten solder. Contrary to the oxide film of Sn, it can promote the fusion of the solder ball and the solder powder in the paste. And, when the total amount of Ag, Cu, Bi, and Ni contents is too large, ΔT increases. Furthermore, the viscosity of the fused solder is too high to damage the fusion of the solder powder of the paste and the solder ball of the BGA. On the other hand, if the total content of Ag, Cu, Bi, and Ni is small, the Ge content will increase relatively, and a hard and brittle Ge oxide will be formed due to thickening, so lack of fusion will occur.

In view of these, in the Sn-Ag-Cu-Bi-Ni-Ge solder alloy, the balance of the total amount of Ag, Cu, Bi, and Ni content and Ge content was investigated in detail to cause fusion. As a result, the insight was gained that non-fusion does not occur when the equilibria are within specific ranges.

(1) The lower limit of the formula must exceed 0.004, preferably at least 0.013, more preferably at least 0.015, more preferably at least 0.018, still more preferably at least 0.019, particularly preferably at least 0.020, most preferably at least 0.021. (1) The upper limit of the formula must be less than 0.032, preferably less than 0.031, more preferably less than 0.030, more preferably less than 0.029, more preferably less than 0.027, most preferably less than 0.026, most preferably less than 0.025, and It may be 0.024 or less, 0.023 or less.

(9) (2) formula The present invention satisfies the following formula (2). Sn×Cu×Ni≦5.0 (2) formula In the above formula (2), Sn, Cu, and Ni are the contents (mass %) of each alloy composition.

In the solder alloy of the present invention, in order to improve the bonding strength of the solder joint, in the compound of Cu and Sn, the compound can be miniaturized by substituting a part of Cu with Ni. In addition, if these elements are well balanced, the viscosity at the time of melting can be controlled so that ΔT does not become too large, and the growth of the Sn compound can be suppressed. As a result, it is presumed that in the Sn-Ag-Cu-Bi-Ni-Ge solder alloy, by containing Sn, Cu and Ni in a well-balanced content, the ΔT is controlled and the intermetallic compound formed at the joint interface becomes finer. , to increase the shear strength.

The upper limit of the formula (2) is 5.0 or less, preferably 4.9 or less, more preferably 4.5 or less, still more preferably 4.0 or less, still more preferably 3.8 or less, particularly preferably 3.7 or less, and most preferably 3.6 or less. 3.3 or less, 3.2 or less. The lower limit of the formula (2) is not particularly limited, but is preferably at least 0.7, more preferably at least 1.0, still more preferably at least 1.3, and still more preferably at least 1.4, from the viewpoint of suppressing Ni corrosion and sufficiently increasing the shear strength. Most preferably, it is 1.5 or more, most preferably, it is 1.6 or more, and may be 2.3 or more, or 2.9 or more.

From the above, the solder alloy of the present invention must satisfy both formula (1) and formula (2) in order to suppress non-fusion and improve shear strength. Thereby, Ni corrosion can also be suppressed.

(10) ΔT If ΔT of the solder alloy of the present invention is within a specific range, the solid-liquid coexistence region will be narrow, and it is preferable in terms of suppressing an increase in the viscosity of molten solder. The range of ΔT is preferably not higher than 100°C, more preferably not higher than 70°C, still more preferably not higher than 40°C.

2. Solder balls The lead-free and antimony-free solder alloy of the present invention is most suitable for the shape of solder balls used in BGA. The true sphericity of the solder ball is preferably above 0.90, more preferably above 0.95, most preferably above 0.99. True sphericity is obtained by various methods such as least square center method (LSC method), minimum zone center method (MZC method), maximum inscribed center method (MIC method), and minimum circumscribed center method (MCC method). In the present invention, the true sphericity of the solder ball is measured using a CNC image measuring system (Ultra Quick Vision ULTRA QV350-PRO measuring device manufactured by MITSUTOYO Corporation) using the minimum zone center method (MZC method). In the present invention, the so-called true sphericity means the deviation from a true sphere. For example, it refers to the arithmetic mean calculated when the diameter of 500 spheres is divided by the major diameter. The closer the value is to the upper limit of 1.00, the closer to a true sphere.

The solder ball of the present invention is used to form bumps on electrodes or substrates of semiconductor packages such as BGA (Ball Grid Array). The diameter of the solder ball of the present invention is preferably in the range of 1-1000 μm, more preferably 50 μm or more and 300 μm. Solder balls can be manufactured by a common solder ball manufacturing method. The diameter in the present invention means the diameter measured by the Ultra Quick Vision ULTRA QV350-PRO measuring device manufactured by MITSUTOYO Corporation.

3. Solder joints The solder joint of the present invention is suitable for use in the connection between an IC chip in a semiconductor package and its substrate (interposer), or in the connection between the semiconductor package and a printed wiring board. The so-called "solder joint" in the present invention refers to the connection between the IC chip and the substrate connected using the above-mentioned solder alloy of the present invention, including the connection between electrodes or the connection between crystal grains and the substrate.

4. Other The joining method using the solder alloy of the present invention may be performed according to a common method using, for example, a reflow method. The heating temperature can be appropriately adjusted according to the heat resistance of the chip or the liquidus temperature of the solder alloy. From the viewpoint of keeping the thermal damage of the wafer low, it is preferably about 240°C. In the case of flow soldering, the melting temperature of the solder alloy is preferably about 20°C above the liquidus temperature. Also, when joining is performed using the solder alloy of the present invention, the microstructure can be made finer in consideration of the cooling temperature at the time of solidification. For example, cool the solder joint at a cooling rate of 2~3°C/s or more. Other joining conditions can be appropriately adjusted according to the alloy composition of the solder alloy.

The solder alloy of the present invention can produce a low-α-quantity alloy by using a low-α-quantity material as its raw material. These low α-intensity alloys can suppress softening errors when used in the formation of solder bumps around memory devices. [Example]

For the solder alloys having the alloy compositions shown in Table 1, ΔT obtained from the liquidus temperature and the solidus temperature without fusion was evaluated as follows. In addition, shear strength and Ni corrosion were also evaluated.

(1) Whether there is no fusion For the solder alloys shown in Table 1, the presence or absence of non-fusion was verified. The verification method is to cast and roll the solder alloy blended with the composition of each example and comparative example to form a small piece of component (2mm (length) × 2mm (width) × 0.1mm (thickness)) by stamping. Shape the chip into a specific size, and place it on a Cu board that has been treated with OSP (Organic Solderability Presevation) coated with flux. , Place it in an environment with a humidity of 100%RH for 24 hours. Furthermore, solder balls (in this example, diameter 300 μm) made of a solder alloy (Sn-3.0Ag-0.5Cu) made of 3.0% Ag, 0.5% Cu, and Sn as the rest, and small chip components Also place it in an environment with a temperature of 125°C and a humidity of 100%RH for 24 hours. Next, flux is coated on the sample made of the solder alloy of the example or the comparative example, and a specific number of solder balls are placed. In this example, the number of solder balls is 9, and 5 pieces are prepared respectively. Next, after reflow, the number of unfused balls was counted to calculate the occurrence rate of poor fusion. The so-called non-fusion refers to the state where the chip and the solder ball are not bonded. When the number of unfused solder balls was 0 or less, it was evaluated as "⊚", when it exceeded 0 and 10 or less, it was evaluated as "◯", and when it exceeded 10, it was evaluated as "×".

(2)ΔT(K) Prepare the solder alloys in Tables 1 and 2, and measure the melting temperature of the solder. As for the measurement method, the solidus temperature was based on JIS Z3198-1. The liquidus temperature is not based on JIS Z3198-1, but is implemented by the same DSC method as the method of measuring the solidus temperature of JIS Z3198-1. The ΔT(K) of the difference between the measured liquidus temperature and the solidus temperature was obtained, and when ΔT(K) was less than 100K, it was marked as "○", and when it exceeded 100K, it was marked as "×".

(3) Shear strength Solder balls with a diameter of 0.6 mm made of the solder shown in Table 1 were produced. Soldering was performed on a substrate with a substrate thickness of 1.2 mm and an electrode size of 0.5 mm in diameter (Cu-OSP) using the solder balls.

Soldering conditions are to apply flux (Senju Metal Industry Co., Ltd.: WF-6400) on the electrode, set the mode of peak temperature 245 ° C, cooling rate 2 ° C / s, use a reflow device (Senju Metal Industry Co., Ltd. Company system: SNR-615) implementation. The prepared sample was subjected to a shear strength test at a shear speed of 1000 mm/s using a shear strength measuring device (manufactured by Nordson Dage: SERIES 4000HS).

(4) Ni Corrosion A preform having a plate thickness of 250 μm and having an alloy composition shown in Table 1 was mounted on a Cu lead frame. Then, an IC chip provided with a backing metal on the substrate bonding surface side of a 5 mm×5 mm×200 μm ^t silicon wafer is mounted on the solder alloy. The backing metal is sequentially laminated with a 0.05 μm Ti layer and a 0.20 μm Ni layer as the barrier layer. The mounting direction refers to the direction in which the Ni layer is in contact with the solder alloy in the IC chip with the metal backing. The substrate carrying the solder alloy and the IC chip is heated in a reflow furnace to a peak temperature of 240°C for die bonding. Next, the section of the obtained lead frame was magnified 30,000 times on the monitor of the SEM, and the average value of the film thickness of the Ni layer was calculated at any 10 positions. The results are shown in Tables 1 and 2.

As shown in Table 1, it can be seen that in Examples 1 to 43 (except for reference examples 11, 13, 17, and 21 to 32), since all alloy compositions satisfy the content of each constituent element, formula (1) and formula (2), Therefore, lack of fusion did not occur, and ΔT was within a specific range. And it was confirmed that the shear strength of the solder joints formed by using the solder alloys of the Examples all showed higher values than those of the Comparative Examples. Furthermore, it was confirmed that Ni corrosion was also suppressed.

On the other hand, since Comparative Examples 1 to 11 did not satisfy the formula (1), many unfused solder balls were detected. And the Sn-2.0Ag-0.75Cu-0.070Ni-0.0080Ge solder alloy (the value represents mass %, the rest is Sn and unavoidable impurities) satisfies the (1) formula, but does not satisfy the (2) formula, so the solder joint Shear strength is poor.

Claims (8)

A lead-free and antimony-free solder, characterized by: in terms of mass %, composed of Ag0.1~4.5%, Cu0.20~0.85%, Bi0.2~5.00%, Ni0.005~0.09%, Ge0.0005~ 0.0045%, the remainder is an alloy composition made of Sn, the above-mentioned alloy composition satisfies the following formula (1) and formula (2), 0.029≦(Ag+Cu+Ni+Bi)×Ge<0.032 (1) formula Sn× Cu×Ni≦5.0 (2) In the above formula (1) and the above formula (2), each of Ag, Cu, Ni, Bi, Ge, and Sn is the content (% by mass) of the alloy composition. The lead-free and antimony-free solder of claim 1, wherein the aforementioned alloy composition, in mass %, contains a group consisting of Mn, Pd, P, Au, Pt, Cr, Fe, Co, V, Mo, and Nb Select one or more of them, and the upper limit of each is 0.01%. A solder ball made of the lead-free and antimony-free solder of claim 1 or 2. The solder ball of claim 3, wherein the average particle size is 1-1000 μm. The solder ball according to claim 3 or 4, wherein the degree of true sphericity is above 0.95. The solder ball according to claim 3 or 4, wherein the degree of true sphericity is above 0.99. A ball grid array formed by using any one of the solder balls in claims 3-6. A solder joint formed by using the lead-free and antimony-free solder of claim 1 or 2.